Monday, March 1, 2010

doing it yourself: how to make a glulam

{In addition to the green building 101 feature, I've decided to add a doing it yourself feature as well. doing it yourself is a theme for our building project... and, who am I kidding, really our approach to life. We do lots and lots of things ourselves that other people hire out. And we sometimes do things ourselves just for the pleasure or curiosity of knowing how it's done or that we can do it. Because this theme is really a reflection of values we hold dear — self-reliance, sustainability, learning new things — I thought I'd share some of what we've learned by doing things ourselves, in hopes that it might be useful or inspiring to someone else.}

The first step to making a glulam is knowing what a glulam is. A glulam is an engineered piece of wood made of glued, laminated timbers. One uses glulams in applications where more wood strength is needed than a standard timber of the same dimensions can provide.

We use a lot of glulams in our house. The ridge beam, the yoke beams, the beams supporting the upper floor, the beams supporting the crow's nest, and a big angled beam that will support the greenhouse.

The greenhouse portion of our house is going to be built using a modified timber moment frame construction technique. We will have 3-1/2" X 3-1/2" posts supported by a floor beam to spread the weight across the brittle masonry and supported horizontally by 3-1/2" X 3-1/2" beams that cross the posts. In between all these timbers will be left openings about 42" X 42" where we will install a glass framing system and insulated glass units to create a wall of glass like you would expect for a greenhouse.

The more typical construction material for moment frames is steel. Steel is super strong in rigidity, compressive strength, and shear strength in relatively small dimensional sizes and is relatively easy to connect and fabricate in all sorts of custom shapes and sizes. However, steel is also a much better thermal conductor than wood and our passive house design depends on eliminating thermal conduction of cold outside air to our warm house. Aluminum is also commonly used in small glass-faced structures like ours (think storefront windows at your local strip mall), but it is even more thermally conductive than steel.

Since we didn't want to use metal for the structural component of our frame, we chose wood as the next most available and cost-effective structural material that is much less thermally conductive. However, we also didn't want to fill the room with the huge unmodified timbers that would have been required to support our greenhouse, so we decided on an engineered wood option.

There are two primary kinds of engineered wood commercially available: glulams and laminated strand lumber products (LSLs, which are marketed under the brand names Timberstrand, LVL, and VersaLam and VersaStud, among others). Both these types of engineered wood products take advantage of the same engineering principle — more than one layer of wood laminated together can make a stronger timber than a non-engineered timber of the same dimensions.

Most of the glulams in our building were purchased from a local lumber shop who in turn got them from a local glulam manufacturer. However, the posts and beams for our greenhouse are a smaller dimension than any of the normally available glulams we can get at the lumber store or from the manufacturer. We could get the posts made out of LSLs, but the posts will be an important architectural element in our greenhouse and we wanted them to match up with the other timbers in our house.

So... the solution? Making our own glulams of the appropriate dimensions, of course! (This is a theme with our house — needing something critical for our home, not being able to find it, and having to make it ourselves.)

The first step of making the glulams was finding the lumber. We needed at least 6 lams per timber and a total of 3-1/2" thickness, which meant that the thickness of each lam needed to be about 5/8" thick. I tried buying 1" X 4" dimensional lumber (which is actually 3/4" X 3-1/2" in real size), but couldn't find them in the same species of wood that all the rest of our framing lumber was. We wanted to keep with our wood species theme, so we had to find another solution. We could find 2" X 4" dimensional wood in the same species, but that meant we had to "re-saw" the lumber. Maybe you remember this picture of us getting some help hauling in all that lumber:

So, re-saw we did. Re-sawing lumber is a challenging task. Because the wood is 3-1/2" thick in the dimension it needs to be cut. There aren't a lot of saws that can cut that deep and be controlled in the way that a long board like that needs to be controlled. The most common tool for re-sawing is the bandsaw. We tried the bandsaw and got at least 1 or 2 boards cut that way, but discovered our bandsaw was not really up to the task.

One of our clever workers created a jig to cut the boards with our fancy, plunge-cut circular saw that cuts 2-3/4" deep. He would cut one side and then turn the board over and cut from the other size. It's pretty much impossible to line the cuts up perfectly, so you can see that there's a sort of seam in the board.

After cutting all the boards down, the board were then thickness planed. Planing is a technique of running blades over a board to make them very, very smooth. Thickness planing also removes material from the board so you can end with the thickness you want. Planing is important so that the surfaces between the lams of wood can be perfectly joined with the glue. Here are some of the results of all this planing.

Next, we waited for a warm-ish day (mid-thirties in the day and mid-twenties lows predicted at night). On this warm day with the heater going, we painted each surface of the lams with weatherproof wood glue and piled 6 of them on top of each other. We painted these with a fairly thick layer of glue to make sure the surface bonding was impeccable.

After painting all these surfaces, but before the glue was set up, we would rush around with innumerable wood clamps getting all the lams perfectly stacked on top of each other and smooshed together so that the glue started to ooze out the seams, alerting us that the lams were adequately glued.

We then allowed the glue to partially set and transported the new glulam to our dry box. After this we went through the whole process all over again until we'd made all the 6 glulams we needed. The dry box was a slapped together invention of rigid foam insulation walls and ceilings and a simple frame to keep the glulams off the ground. We closed them up, aimed the heater on them, and kept them warm for the duration of the curing time.

Next, the newly cured glulams will be thickness planed in their composite state to get them all to the 3-1/2" X 3-1/2" final size.

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